From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id EED6EC433F5 for ; Wed, 13 Apr 2022 15:47:30 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S236677AbiDMPtu convert rfc822-to-8bit (ORCPT ); Wed, 13 Apr 2022 11:49:50 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:43656 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S236672AbiDMPtq (ORCPT ); Wed, 13 Apr 2022 11:49:46 -0400 Received: from out03.mta.xmission.com (out03.mta.xmission.com [166.70.13.233]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 2DC2D66214 for ; Wed, 13 Apr 2022 08:47:23 -0700 (PDT) Received: from in01.mta.xmission.com ([166.70.13.51]:59624) by out03.mta.xmission.com with esmtps (TLS1.3) tls TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 (Exim 4.93) (envelope-from ) id 1nefDF-0062ZF-FB; Wed, 13 Apr 2022 09:47:21 -0600 Received: from ip68-227-174-4.om.om.cox.net ([68.227.174.4]:60598 helo=email.froward.int.ebiederm.org.xmission.com) by in01.mta.xmission.com with esmtpsa (TLS1.3) tls TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 (Exim 4.93) (envelope-from ) id 1nefDD-00FrVt-4O; Wed, 13 Apr 2022 09:47:20 -0600 From: "Eric W. Biederman" To: Zhang Qiao Cc: lkml , , , Peter Zijlstra , , , , References: Date: Wed, 13 Apr 2022 10:47:12 -0500 In-Reply-To: (Zhang Qiao's message of "Wed, 13 Apr 2022 09:56:29 +0800") Message-ID: <87ilrd2dfj.fsf@email.froward.int.ebiederm.org> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/27.1 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8BIT X-XM-SPF: eid=1nefDD-00FrVt-4O;;;mid=<87ilrd2dfj.fsf@email.froward.int.ebiederm.org>;;;hst=in01.mta.xmission.com;;;ip=68.227.174.4;;;frm=ebiederm@xmission.com;;;spf=neutral X-XM-AID: U2FsdGVkX183uWT3/BdaXd5sHej2Mh09utR4YSt9oPM= X-SA-Exim-Connect-IP: 68.227.174.4 X-SA-Exim-Mail-From: ebiederm@xmission.com Subject: Re: Question about kill a process group X-SA-Exim-Version: 4.2.1 (built Sat, 08 Feb 2020 21:53:50 +0000) X-SA-Exim-Scanned: Yes (on in01.mta.xmission.com) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Zhang Qiao writes: > Gentle ping. Any comments on this problem? Is fork12 a new test? Is there a real world use case that connects to this? How many children are being created in this test? Several million? I would like to blame this on the old issue that tasklist_lock being a global lock. Given the number of child processes (as many as can be created) I don't think we are hurt much by using a global lock. The problem for solubility is that we have a lock. Fundamentally there must be a lock taken to maintain the parent's list of children. I only see SIGQUIT being called once in the parent process so that should not be an issue. There is a minor issue in fork12 that it calls exit(0) instead of _exit(0) in the children. Not the problem you are dealing with but it does look like it can be a distraction. I suspect the issue really is the thundering hurd of a million+ processes synchronizing on a single lock. I don't think this is a hard lockup, just a global slow down. I expect everything will eventually exit. To do something about this is going to take a deep and fundamental redesign of how we maintain process lists to handle a parent with millions of children well. Is there any real world reason to care about this case? Without real world motivation I am inclined to just note that this is something that is handled poorly, and leave it as is. Eric > > 在 2022/4/2 10:22, Zhang Qiao 写道: >> ping... >> >> Any suggestions for this problem？ >> >> thank! >> Qiao >> >> >> 在 2022/3/29 16:07, Zhang Qiao 写道: >>> hello everyone, >>> >>> I got a hradlockup panic when run the ltp syscall testcases. >>> >>> 348439.713178] NMI watchdog: Watchdog detected hard LOCKUP on cpu 32 >>> [348439.713236] irq event stamp: 0 >>> [348439.713237] hardirqs last enabled at (0): [<0000000000000000>] 0x0 >>> [348439.713238] hardirqs last disabled at (0): [] copy_process+0x7f5/0x2160 >>> [348439.713239] softirqs last enabled at (0): [] copy_process+0x7f5/0x2160 >>> [348439.713240] softirqs last disabled at (0): [<0000000000000000>] 0x0 >>> [348439.713241] CPU: 32 PID: 1151212 Comm: fork12 Kdump: loaded Tainted: G S 5.10.0+ #1 >>> [348439.713242] Hardware name: Huawei RH2288H V3/BC11HGSA0, BIOS 3.35 10/20/2016 >>> [348439.713243] RIP: 0010:queued_write_lock_slowpath+0x4d/0x80 >>> [348439.713245] RSP: 0018:ffffa3a6bed4fe60 EFLAGS: 00000006 >>> [348439.713246] RAX: 0000000000000500 RBX: ffffffff892060c0 RCX: 00000000000000ff >>> [348439.713247] RDX: 0000000000000500 RSI: 0000000000000100 RDI: ffffffff892060c0 >>> [348439.713248] RBP: ffffffff892060c4 R08: 0000000000000001 R09: 0000000000000000 >>> [348439.713249] R10: ffffa3a6bed4fde8 R11: 0000000000000000 R12: ffff96dfd3b68001 >>> [348439.713250] R13: ffff96dfd3b68000 R14: ffff96dfd3b68c38 R15: ffff96e2cf1f51c0 >>> [348439.713251] FS: 0000000000000000(0000) GS:ffff96edbc200000(0000) knlGS:0000000000000000 >>> [348439.713252] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 >>> [348439.713253] CR2: 0000000000416ea0 CR3: 0000002d91812004 CR4: 00000000001706e0 >>> [348439.713254] Call Trace: >>> [348439.713255] do_raw_write_lock+0xa9/0xb0 >>> [348439.713256] _raw_write_lock_irq+0x5a/0x70 >>> [348439.713256] do_exit+0x429/0xd00 >>> [348439.713257] do_group_exit+0x39/0xb0 >>> [348439.713258] __x64_sys_exit_group+0x14/0x20 >>> [348439.713259] do_syscall_64+0x33/0x40 >>> [348439.713260] entry_SYSCALL_64_after_hwframe+0x44/0xa9 >>> [348439.713260] RIP: 0033:0x7f59295a7066 >>> [348439.713261] Code: Unable to access opcode bytes at RIP 0x7f59295a703c. >>> [348439.713262] RSP: 002b:00007fff0afeac38 EFLAGS: 00000246 ORIG_RAX: 00000000000000e7 >>> [348439.713264] RAX: ffffffffffffffda RBX: 00007f5929694530 RCX: 00007f59295a7066 >>> [348439.713265] RDX: 0000000000000002 RSI: 000000000000003c RDI: 0000000000000002 >>> [348439.713266] RBP: 0000000000000002 R08: 00000000000000e7 R09: ffffffffffffff80 >>> [348439.713267] R10: 0000000000000002 R11: 0000000000000246 R12: 00007f5929694530 >>> [348439.713268] R13: 0000000000000001 R14: 00007f5929697f68 R15: 0000000000000000 >>> [348439.713269] Kernel panic - not syncing: Hard LOCKUP >>> [348439.713270] CPU: 32 PID: 1151212 Comm: fork12 Kdump: loaded Tainted: G S 5.10.0+ #1 >>> [348439.713272] Hardware name: Huawei RH2288H V3/BC11HGSA0, BIOS 3.35 10/20/2016 >>> [348439.713272] Call Trace: >>> [348439.713273] >>> [348439.713274] dump_stack+0x77/0x97 >>> [348439.713275] panic+0x10c/0x2fb >>> [348439.713275] nmi_panic+0x35/0x40 >>> [348439.713276] watchdog_hardlockup_check+0xeb/0x110 >>> [348439.713277] __perf_event_overflow+0x52/0xf0 >>> [348439.713278] handle_pmi_common+0x21a/0x320 >>> [348439.713286] intel_pmu_handle_irq+0xc9/0x1b0 >>> [348439.713287] perf_event_nmi_handler+0x24/0x40 >>> [348439.713288] nmi_handle+0xc3/0x2a0 >>> [348439.713289] default_do_nmi+0x49/0xf0 >>> [348439.713289] exc_nmi+0x146/0x160 >>> [348439.713290] end_repeat_nmi+0x16/0x55 >>> [348439.713291] RIP: 0010:queued_write_lock_slowpath+0x4d/0x80 >>> [348439.713293] RSP: 0018:ffffa3a6bed4fe60 EFLAGS: 00000006 >>> [348439.713295] RAX: 0000000000000500 RBX: ffffffff892060c0 RCX: 00000000000000ff >>> [348439.713296] RDX: 0000000000000500 RSI: 0000000000000100 RDI: ffffffff892060c0 >>> [348439.713296] RBP: ffffffff892060c4 R08: 0000000000000001 R09: 0000000000000000 >>> [348439.713297] R10: ffffa3a6bed4fde8 R11: 0000000000000000 R12: ffff96dfd3b68001 >>> [348439.713298] R13: ffff96dfd3b68000 R14: ffff96dfd3b68c38 R15: ffff96e2cf1f51c0 >>> [348439.713300] >>> [348439.713301] do_raw_write_lock+0xa9/0xb0 >>> [348439.713302] _raw_write_lock_irq+0x5a/0x70 >>> [348439.713303] do_exit+0x429/0xd00 >>> [348439.713303] do_group_exit+0x39/0xb0 >>> [348439.713304] __x64_sys_exit_group+0x14/0x20 >>> [348439.713305] do_syscall_64+0x33/0x40 >>> [348439.713306] entry_SYSCALL_64_after_hwframe+0x44/0xa9 >>> [348439.713307] RIP: 0033:0x7f59295a7066 >>> [348439.713308] Code: Unable to access opcode bytes at RIP 0x7f59295a703c. >>> >>> >>> when analyzing vmcore, i notice lots of fork12 processes are waiting for tasklist read lock or write >>> lock (see the attachment file all_cpu_stacks.log)，and every fork12 process(belongs to the same >>> process group) call kill(0, SIGQUIT) in their signal handler()[1], it will traverse all the processes in the >>> same process group and send signal to them one by one, which is a very time-costly work and hold tasklist >>> read lock long time. At the same time, other processes will exit after receive signal, they try to get >>> the tasklist write lock at exit_notify(). >>> >>> [1] fork12 testcase: https://github.com/linux-test-project/ltp/blob/master/testcases/kernel/syscalls/fork/fork12.c >>> >>> some processes call kill(0, SIGQUIT), wait for tasklist read lock: >>> >>> #5 [ffff972a9b16fd78] native_queued_spin_lock_slowpath at ffffffff9931ed47 >>> #6 [ffff972a9b16fd78] queued_read_lock_slowpath at ffffffff99320a58 >>> #7 [ffff972a9b16fd90] do_wait at ffffffff992bc17d >>> #8 [ffff972a9b16fdd0] kernel_wait4 at ffffffff992bd88d >>> #9 [ffff972a9b16fe58] __do_sys_wait4 at ffffffff992bd9e5 >>> #10 [ffff972a9b16ff30] do_syscall_64 at ffffffff9920432d >>> #11 [ffff972a9b16ff50] entry_SYSCALL_64_after_hwframe at ffffffff99c000ad >>> >>> As the same time, some processes are exiting, wait for tasklist write lock: >>> >>> #5 [ffff972aa49a7e60] native_queued_spin_lock_slowpath at ffffffff9931ecb0 >>> #6 [ffff972aa49a7e60] queued_write_lock_slowpath at ffffffff993209e4 >>> #7 [ffff972aa49a7e78] do_raw_write_lock at ffffffff99320834 >>> #8 [ffff972aa49a7e88] do_exit at ffffffff992bcd78 >>> #9 [ffff972aa49a7f00] do_group_exit at ffffffff992bd719 >>> #10 [ffff972aa49a7f28] __x64_sys_exit_group at ffffffff992bd7a4 >>> #11 [ffff972aa49a7f30] do_syscall_64 at ffffffff9920432d >>> #12 [ffff972aa49a7f50] entry_SYSCALL_64_after_hwframe at ffffffff99c000ad >>> >>> In this scenario,there are lots of process are waiting for tasklist read lock or the tasklist >>> write lock, so they will queue. if the wait queue is long enough, it might cause a hardlockup issue when a >>> process wait for taking the write lock at exit_notify(). >>> >>> I tried to solve this problem by avoiding traversing the process group multiple times when kill(0, xxxx) >>> is called multiple times form the same process group, but it doesn't look like a good solution. >>> >>> Is there any good idea for fixing this problem ? >>> >>> Thanks! >>> >>> Qiao >>> . >>> >> . >>